In the construction of turbomachines, in particular in the construction of steam turbines, these machines are designed in such a manner that a seal is provided, such that no ambient air can penetrate into the steam turbine. For this purpose, use is made of seals of varying type. By way of example, sealing steam is used to prevent the admission of the air into the turbine. However, the sealing steam used for this purpose is taken from the steam circuit and therefore does not contribute to the energy conversion, and this has the effect that the efficiency of the turbine set as a whole is impaired.
FIG. 1 shows the known prior art. A steam turbine 4 designed for low pressure is supplied with live steam via an inflow opening 10. The generation of the live steam is not shown in greater detail in FIG. 1. Some of the live steam is guided on a branch line 11 via a bleed line 7a to the seal 9. The bleed line 7a is accordingly in the form of a sealing steam line 12 and therefore guides sealing steam into a sealing steam region 13. In the sealing steam region 13, the sealing steam moves to the left and to the right through seals, a flow of the sealing steam to the left leading into a vapor steam chamber 14. A slightly lower pressure prevails in this vapor steam chamber 14 than in the surroundings, and therefore a vapor steam extraction system 8 extracts the mixture of air taken in from the surroundings and the steam conducted from the sealing steam region 13. As a result, steam conducted in the steam turbine 4 cannot escape into the surroundings.
The steam, the thermal energy of which is converted into mechanical energy in the steam turbine 4, flows via an outlet opening 15 to a condenser 5. The steam condenses in the condenser 5 to form water and is fed back to the water vapor circuit via a pump 6. The pressure of the sealing steam is above the pressure of the atmosphere. In order to keep the demand for sealing steam and the associated losses as low as possible, seals with the greatest possible efficiency are installed. This can be effected using seals of a large structural length or using high-efficiency sealing systems, e.g. brush seals. The documents U.S. Pat. No. 6,918,252, DE 43 13 805, U.S. Pat. No. 4,191,021 and DE 10 2007 037311 disclose various possibilities in relation to the sealing.